Obama's security quickly checked to discover the cause of the problem, before security vehicles drove in to block the public's view of the incident.

"I think it was really the comedy of it," one onlooker told BBC News. "There was so much drama with the guys in the secret service, and for them to come out at the final moment and we were expected to wave - and to hear the big bang!"

She added: "I think there was a degree of shock."

Obama's car later left the embassy via a different gate to cheering from the amused onlookers.